Communication disorders affect millions of people. Understanding the neural bases of vocal learning will enable early diagnosis and effective treatment of these diseases. There are a few nonhuman vocal learners, of which the songbirds offer the best characterized model in terms of physiology and behavior. As with humans, the zebra finch songbird learns its song in two phases: a sensory phase during which the song of an adult tutor is memorized and a sensorimotor phase during which the bird's own vocalizations are shaped through auditory feedback to match the tutor song. The shaping of the vocalization requires that the comparison between auditory feedback and the memory of the tutor song somehow impact the song motor control circuitry. We recently found that the tutor song selectively activates a key nucleus of the song premotor pathway (Nick, 2003). This selective activation occurs only during waking and only during the period of development when the tutor song memory is used to shape vocalizations. This suggests that the comparison of auditory feedback with the tutor song memory generates a matching signal that is relayed to the premotor nucleus. Three related hypotheses will be tested at the level of single neurons: (1) responses of individual neurons convey the degree of similarity between stimuli and the tutor song memory; (2) the putative matching signal occurs during singing behavior; and (3) the putative matching signal is relayed to the basal ganglia, which is affected in many human diseases. The proposed experiments are designed to avoid approaches that have confounded previous experiments, such as the use of anesthesia. The study will utilize two powerful techniques: multi-electrode recording, which enables the stable assessment of the activity of many single neurons, and juxtacellular recording and dye filling, which enables the identification of individual recorded neurons. The long-term goals of this project will use the putative matching signal to illuminate the role of memory and sensation in shaping vocal behavior. [unreadable] [unreadable]